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Holey fiber creates convenient OPO

13 May 2004

A UK-Danish partnership report a continuous-wave all-fiber optical parametric oscillator.

A team from Imperial College, UK and the Danish firm Crystal Fibre claims to have made the first continuous wave (cw) all-fiber optical parametric oscillator (OPO) using a holey fiber (Optics Letters 29 983).

Although similar devices have been made before, Christiano de Matos from Imperial’s femtosecond optics group told Optics.org that this is the first version that is fully fiber integrated and offers a cw output.

Fiber-based OPOs are attractive because they offer a compact, tunable alternative to solid-state lasers and are virtually alignment free. “When optimised, the system is a potential substitute for solid state lasers,” said de Matos. “For example, its tunable signal could be used in spectroscopy or telecoms WDM [wavelength division multiplexing] systems.”

The Imperial prototype operates at a wavelength of 1.55 µm and emits signal and idler powers in the region of 1 mW. It also boasts a 30 dB extinction ratio and a 10 pm linewidth.

The setup is based on a unidirectional ring cavity containing a 100 m length of holey fiber with a 2.3 µm core diameter and an estimated modal area of 7 µm2. An output coupler extracting 1% of the cavity power, a polarization controller, a fiber Bragg grating and broadband optical circulator are also inserted into the ring. The optical circulator is used to introduce the pump light from a semiconductor laser seeded erbium-doped fiber amplifier into the cavity.

De Matos attributes their success to three key elements of the design - the use of a high power (3.5 W) pump, refinement of their fiber splicing technique (the lowest splice loss was 0.42 dB) and state-of-the-art microstructured fiber.

James Tyrrell is reporter on Optics.org and Opto & Laser Europe magazine.

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